Method and apparatus for encoding or decoding video data with sub-pixel motion vector refinement

Abstract

A method and a device for encoding or decoding video data. It concerns more particularly the encoding according to a particular encoding mode using a decoder side motion vector derivation mode referenced as frame-rate up conversion mode or FRUC mode. In FRUC merge mode, the derivation process comprises a refinement step to increase the accuracy of the obtained motion vector at the sub-pixel level. This process involves the evaluation of different sub-pixel position around the obtained motion vector according to different patterns. The present invention has been devised to improve the known refinement step. It aims at improving the coding efficiency by considering the characteristics of the matching type and/or the signal inside the templates.

The invention claimed is: 
     
       1. A method for decoding video data comprising frames, each frame being split into blocks, the method for decoding comprising:
 determining whether a first mode is used, the first mode being a mode in which at least refinement for a motion vector related to a block to be decoded is capable of being performed in the method for decoding; 
 determining, in a case where the first mode is used, whether to perform the refinement for the motion vector, based on at least sample values of the video data in an area different from the block to be decoded; 
 refining the motion vector related to the block to be decoded, in a case where it is determined that the refinement is performed; and 
 decoding the block using an inter prediction using the refined motion vector, in a case where the refinement is performed, wherein inverse transformation is used for decoding the block of pixels, 
 wherein a plurality of patterns for refining is capable of being used in the first mode in the method for decoding; 
 wherein the plurality of patterns includes a horizontal pattern and a vertical pattern, 
 wherein, when using the horizontal pattern, a plurality of horizontal sub-pixel positions on the right of a position to be refined and a plurality of horizontal sub-pixel positions on the left of the position to be refined are candidates of a horizontal position of the refined motion vector, and 
 wherein, when using the vertical pattern, a plurality of vertical sub-pixel positions above the position to be refined and a plurality of vertical sub-pixel positions below the position to be refined are candidates of a vertical position of the refined motion vector. 
 
     
     
       2. The method of  claim 1 , wherein the refined motion vector is at 1/16 sub-pixel accuracy. 
     
     
       3. The method of  claim 1 , wherein sample values in the block to be decoded are not used to determine whether to perform the refinement. 
     
     
       4. An apparatus for decoding video data comprising frames, each frame being split into blocks, the apparatus for decoding video data comprising one or more processors configured to decode a block of pixels by:
 determining whether a first mode is used, the first mode being a mode in which at least refinement for a motion vector related to a block to be decoded is capable of being performed in the apparatus for decoding; 
 determining, in a case where the first mode is used, whether to perform the refinement for the motion vector, based on at least sample values of the video data in an area different from the block to be decoded; 
 refining the motion vector related to the block to be decoded, in a case where it is determined that the refinement is performed; and 
 decoding the block using an inter prediction using the refined motion vector, in a case where the refinement is performed, wherein inverse transformation is used for decoding the block of pixels, 
 wherein a plurality of patterns for refining is capable of being used in the first mode by the apparatus for decoding, 
 wherein the plurality of patterns includes a horizontal pattern and a vertical pattern, 
 wherein, when using the horizontal pattern, a plurality of horizontal sub-pixel positions on the right of a position to be refined and a plurality of horizontal sub-pixel positions on the left of the position to be refined are candidates of a horizontal position of the refined motion vector, and 
 wherein, when using the vertical pattern, a plurality of vertical sub-pixel positions above the position to be refined and a plurality of vertical sub-pixel positions below the position to be refined are candidates of a vertical position of the refined motion vector. 
 
     
     
       5. The apparatus of  claim 4 , wherein the refined motion vector is at 1/16 sub-pixel accuracy. 
     
     
       6. The apparatus of  claim 4 , wherein sample values in the block to be decoded are not used to determine whether to perform the refinement. 
     
     
       7. A non-transitory computer-readable storage medium storing instructions of a computer program for implementing a method for decoding video data comprising frames, each frame being split into blocks, the method for decoding comprising:
 determining whether a first mode is used, the first mode being a mode in which at least refinement for a motion vector related to a block to be decoded is capable of being performed in the method for decoding; 
 determining, in a case where the first mode is used, whether to perform the refinement for the motion vector, based on at least sample values of the video data in an area different from the block to be decoded; 
 refining the motion vector related to the block to be decoded, in a case where it is determined that the refinement is performed; and 
 decoding the block using an inter prediction using the refined motion vector, in a case where the refinement is performed, wherein inverse transformation is used for decoding the block of pixels, 
 wherein a plurality of patterns for refining is capable of being used in the first mode in the method for decoding; 
 wherein the plurality of patterns includes a horizontal pattern and a vertical pattern, 
 wherein, when using the horizontal pattern, a plurality of horizontal sub-pixel positions on the right of a position to be refined and a plurality of horizontal sub-pixel positions on the left of the position to be refined are candidates of a horizontal position of the refined motion vector, and 
 wherein, when using the vertical pattern, a plurality of vertical sub-pixel positions above the position to be refined and a plurality of vertical sub-pixel positions below the position to be refined are candidates of a vertical position of the refined motion vector.